The invention relates to a fuel injection apparatus for internal combustion engines, particularly for diesel engines.
In such fuel injection apparatus, the cut-off device serves to terminate the fuel injection as suddenly as possible during the occurrence of disturbances or errors. For this purpose, it is necessary not only to stop the delivery output of the delivery pump to the suction chamber of the fuel injection pump, but also to prevent the continued delivery of fuel from the suction chamber to the injection nozzles. The latter is no longer the case when the suction chamber pressure drops below 0.2 bar absolute, since the pump element of the fuel injection pump is then no longer sufficiently filled with fuel.
In a known fuel injection apparatus (DE-A-21 45 983), the cut-off device comprises a shut-off valve, which is constructed as a disk valve, and a suction pump which are combined to form a constructional unit. The suction pump comprises a plunger displaceable in a storage space and a pressure spring which acts upon the plunger. In normal operation, a mechanical locking device holds the plunger in a sliding out position when the pressure spring is tensioned, in which sliding out position the storage volume of the storage space is virtually zero. In this position, the disk valve is held by the plunger in the open position against the force of a valve closing spring via a valve tappet When the disk valve is open, the fuel delivered by the delivery pump arrives in the space defined by the plunger, in which the plunger pressure spring is arranged and flows out into the suction chamber When a cut-off is effected, the locking device is released The plunger is displaced by the plunger pressure spring and releases the storage space. A vacuum pressure accordingly arises in the line between the cut-off device and the suction chamber which prevents additional fuel from reaching the suction chamber of the injection pump. The plunger, sliding back in the storage space, also releases the disk valve, which moves into its closing position under the action of its valve closing spring. The delivery pump is blocked by the suction chamber and delivers back into the fuel tank via an overflow valve.